A variety of digital signal processing algorithms are used for detecting the presence of an expected signal within a received noisy signal. When the expected signal is a single tone (pure sine wave at a particular frequency), the power spectral density (PSD) algorithm is commonly used. The presence of a single tone is revealed by a single spike in PSD at the tone frequency when PSD is plotted versus frequency.
The probability of detection depends on the signal-to-noise ratio (SNR) of the received signal, with the typical probability of tone detection dropping rapidly when SNR drops below −10 dB. Therefore, improvements to tone detection are desirable.